Speaker systems with integral amplification electronics provide simple, compact audio transducers for multimedia personal computers. These speaker systems, referred to herein as multimedia computer speaker systems, typically include pairs of wide-band speaker drivers mounted in separate housings with amplification electronics incorporated into one or both housings. Because compactness is desirable, small, wide-band speaker drivers (e.g., 3-inch diameter cone speaker drivers) are commonly used.
Many conventional multimedia computers include two-channel (stereo) multimedia computer audio sub-systems. Typically, a conventional two-channel multimedia computer audio sub-system includes a two-channel audio sub-sub-system control circuit, which is commonly configured as a separate computer expansion board called a “sound card,” and two wide-band audio transducers or speakers. A sub-woofer audio transducer or speaker is also included in many implementations. Conventional two-channel audio sub-systems are configured to provide at the two wide-band speakers distinct audio playback according to two distinct audio channels included in a multimedia computer work such as a game, music, etc.
Some multimedia computers now include four-channel multimedia computer audio sub-systems, sometimes called surround sound systems, environmental audio systems, or multi-channel audio systems. A four-channel multimedia computer audio sub-system includes a multimedia computer speaker system with four wide-band audio transducers or speakers, and typically a sub-woofer audio transducer or speaker. The four wide-band speakers receive four different audio signals or channels. The four-channel multimedia computer audio sub-system may include a two- or a four-channel audio-sub-system control circuit (e.g., sound card). Some four-channel multimedia computer audio sub-systems include four-channel audio sub-system control circuits that are adapted for multimedia computer works with four distinct audio channels. Exemplary audio sub-system control circuits of this type are promulgated as the Monster Sound™ sound cards from Diamond Multimedia Systems, Inc., the Montego II Quadzilla sound card from Voyetra Turtle Beach, Inc., and the Sound Blaster LIVE sound cards from Creative Technology Ltd. The four distinct audio signals may be referred to as right front, right rear, left front, and left rear. A subwoofer audio signal is generally a summed and low-pass filtered combination of at least two of the four distinct audio channels.
In this type of system, the wide-band speakers are positioned to surround a user of a multimedia computer with two pairs of wide-band speakers, one each in front of and behind the user. The sub-woofer generates audio outputs of such low frequencies that the user is unable to discern the direction of those sounds. As a result, the positioning of the sub-woofer is generally arbitrary.
Earlier four-channel multimedia computer audio sub-systems were of the matrix-encoded type. Simple matrix-encoded four-channel multimedia computer audio sub-systems were sometimes adapted from a conventional two-channel stereo sub-system. Front right and front left speakers would receive conventional right and left stereo audio signals. Rear right and rear left speakers both would receive a difference (e.g., Right-Left) between the two stereo signals.
A disadvantage of such a simple matrix-encoded system is that the rear speakers receive the same audio signal (e.g., Right-Left), and the audio signal is asymmetric as to the right and left stereo audio signals. This can cause a user to perceive different sounds as emanating from incongruous locations. (A user's perceptions of where sounds originate is sometimes called the sound image.)
For example, an audio signal that includes only right channel sound and no left channel sound would be played at the right front speaker and both rear speakers. These three speakers would form an audio image for the user that makes the sound seem to come from behind and to the right of the user. An audio signal that includes only left channel sound and no right channel sound would be played at the left front speaker, and the inverse of the sound would be played at both rear speakers. These three speakers would form an audio image for the user that makes the sound seem to come from behind and to the left of the user, but shifted because of the inverse left channel sounds played in the rear speakers. Such sound image incongruities are undesirable.
Another example of a four-channel multimedia computer audio sub-system is the Dolby™ surround encoding promulgated by Dolby Laboratories, Inc. This type of four-channel multimedia computer audio sub-system includes two matrix-encoded audio channels. A first channel includes a right-side audio channel, a center audio channel, and a surround audio channel. A second channel includes a left-side audio channel, the center audio channel, and the inverse of the surround audio channel. The first and second channels may be represented as:Channel 1=Right+Center−SurroundChannel 2=Left+Center+Surround
In this type of system, Channel 1 and Channel 2 function as the right- and left-side audio channels that are applied to wide-band speakers that are positioned to the respective right and left of the user. A Center audio channel corresponds to a wide-band speaker that is positioned centrally in front of the user and is decoded as the sum of the Channel 1 and Channel 2 signals, resulting in the Center audio channel including the following audio components:Right+Left+2Center.A Surround audio channel corresponds to a wide-band speaker that is positioned centrally behind the user and is decoded as the difference of the Channel 1 and Channel 2 signals, resulting in the Surround audio channel including the following audio components:Right−Left+2 SurroundA disadvantage of such systems is that the Right, Left, Center, and Surround audio channels cannot be isolated from each other. In particular, the Right or Left channels cannot be separated from the Surround or Center Channels.
Most matrixed and distinct four-channel audio sub-systems are configured to provide at the wide-band speakers audio playback according to four distinct audio channels included in a multimedia computer work such as a game, music, etc. The four distinct audio channels provide a surround sound playback with acoustic characteristics that are perceivably enhanced beyond those of traditional stereophonic playback.
A vast majority of computers include audio sub-system control circuits (e.g., “sound cards”) that support only two audio channels (i.e., stereo). If a multimedia computer work having four distinct audio channels adapted to a four-channel audio sub-system is played on a conventional stereo audio sub-system control circuit, only two of the channels in the work will be played. Even if four speakers are driven by the conventional stereo audio sub-system control circuit, both right side speakers typically will play the same right-side audio signal, and both left side speakers typically will play the same left-side audio signal. Similarly, if a multimedia computer work having four matrixed audio channels (e.g., Dolby™ surround encoding) is played on a conventional stereo audio sub-system control circuit, only the two matrixed channels in the work will be played (e.g., Channel 1 and Channel 2). Even if four speakers are driven by the conventional stereo audio sub-system control circuit, both right side speakers typically will play the same right-side audio signal, and both left side speakers typically will play the same left-side audio signal. The exception to this is if the multimedia computer speaker system contains a matrix decoding circuit such as the Dolby™ Surround decoder.
Accordingly, multimedia computer works having four distinct audio channels adapted to four-channel audio sub-systems provide no audio improvement when played with conventional stereo audio sub-system control circuits. As a consequence, users having computer systems with conventional stereo audio sub-system control circuits enjoy no benefits from multimedia computer works having four distinct or matrixed audio channels, and the market for such works remains correspondingly limited.
The present invention includes a universal four-channel multimedia computer speaker system that is connectable to audio sub-system control circuits (e.g., “sound cards”) of both the four-channel type and the conventional two-channel (stereo) type. The universal four-channel multimedia computer speaker system provides an actual four-channel surround sound playback whenever such playback is supported by the audio sub-system control circuit and a multimedia work with four distinct audio channels. If the audio sub-system control circuit or the multimedia work does not support four-channel surround sound playback for four distinct audio channels, the universal four-channel multimedia computer speaker system provides a proxy surround sound playback that simulates surround sound playback without suffering from incongruous sound image artifacts characteristic of some prior systems.
With the audio sub-system control circuit being of a distinct four-channel type, the universal four-channel speaker system is configured to provide at four wide-band speakers distinct audio playback according to four distinct audio channels in a four audio channel multimedia computer work such as a game, music, etc. In this configuration, the universal four-channel speaker system functions as a conventional multimedia computer four-channel surround sound audio sub-system system.
For a multimedia computer work with four distinct or matrixed audio channels, and the audio sub-system control circuit being of a conventional two-channel (stereo) type, the universal four-channel speaker system is configured to provide one pair of wide-band speakers (e.g., the front) with distinct audio playback according to respective right-front and left-front audio channels in a four audio channel multimedia computer work such as a game, music, etc. The universal four-channel speaker system is configured to provide at the rear speakers distinct audio playback that is generated from the right-front and left-front audio channels in the four audio channel multimedia computer work. With respect to the rear speakers, the universal four-channel speaker system includes a proxy audio signal component that provides respective right and left rear proxy audio signals to proximate the typical sound of actual right and left rear audio signals carried on a four audio channel multimedia computer work.
In one implementation, the proxy audio signal component generates the right and left rear proxy audio signals as inverse differences of the right-front and left-front audio channels in the four audio channel multimedia computer work. The inverse differences form the right and left rear proxy audio signals symmetrically with respect to the right-front and left-front audio channels, thereby eliminating the incongruous sound images that could arise in prior systems. The proxy audio signal component is enclosed in a housing that may or may not also enclose one of the speakers of the speaker system.
Additional objects and advantages of the present invention will be apparent from the detailed description of the preferred embodiment thereof, which proceeds with reference to the accompanying drawings.